1. Field of the Invention
The present invention generally relates to an etching technique in the semiconductor manufacture, and more particularly relates to a method for forming a rounded corner of a contact window and a via by using a two-step light etching technique.
2. Description of the Prior Art
In view of the effect of the etching process is remove the non-photoresist-covered and non-protected portion of the membrane by using chemical reaction method or physics way, wherein the membrane is deposited before the photolithograph process and has a thickness between about thousands of angstroms or hundreds of angstroms. In other word, the device pattern of the photo-mask is transferred on the photoresist by the photolithograph process and then transferred to the membrane by the etching process.
In the semiconductor manufacture, the contact between metal layer and silicon surface and the contact between different metal layers are formed by the way of the interconnection according to the metallization process. In general, the contact between metal layer and silicon surface is so-called a contact window and the contact between different metal layers is so-called a via. With the increased density of integrated circuit, the interconnection technique becomes more and more important so as the formulation of the contact window or via also becomes more and more important.
To make an example of the fabrication of the MOS contact window, referring to the FIG. 1A, the figure is a schematic representation structure during the formulation of a contact window. First, a silicon substrate 10 is provided with some basic devices, such as MOS transistors, therein and a dielectric layer 12 is uniformly overlaid on the silicon substrate 10. Then, a patterned photoresist layer 14 is formed on the dielectric layer 12 by photolithograph technique, wherein the photolithograph process comprises the steps of defining the contact window location by the photo-mask, then combining with the MOS etching technique, such as plasma etching process, to form the contact window 16, and removing the patterned photoresist layer 14 to form a contact window for the use of metal-filling, such as shown in the FIG. 1B.
For the purpose of improved metal-filling, after completing the contact window 16 and removing the photoresist layer 14, the conventional method utilizes the higher energy ion to strike the opening of the contact window 16 to achieve the object of the top corner rounding, such as shown in the FIG. 1C. However, the method for rounding the top corner with the higher energy ion will easily cause the disadvantages of charge induced damage and bottom layer loss. Furthermore, it will cause the effect of the bowling profile.
Obviously, the main spirit of the present invention is to provide a fabrication method for forming a rounded opening of a contact window and a via by using a two-step light etching technique, and then some disadvantages of well-known technology are overcome.
The primary object of the present invention is to provide a fabrication method for forming a rounded corner of a contact window and a via hole by using a two-step light etching technique and supply for following metal-filling process.
Another object of the present invention is to utilize oxygen plasma, which are full of neutral radical and lower energy ion, and fluorocarbon plasma to complete the two-step light etching process. The present invention not only can achieve the object of the rounded corner of a contact window or a via, but also can overcome some disadvantages of charge induced damage and bottom layer loss resulting in prior technology.
A further object of the present invention is to provide a method for forming a rounded corner of a contact window and a via hole by using a two-step light etching technique with visible equipments.
In order to achieve previous objects, the present invention comprises the steps of: forming a flat dielectric layer on a semiconductor device; forming a photoresist layer on the dielectric layer; and etching the dielectric layer by using the photoresist layer as a mask to form a contact window. In the present invention, a first step etching process is performed to remove a portion of the photoresist layer adjacent to the opening of the contact window so as to expose a portion of said dielectric layer adjacent to the contact window; and a second-step etching process is performed to round the exposed portion of the dielectric layer to form a rounded profile of the opening of the contact window; and then to remove the photoresist layer thereon.
Other advantages will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of the present invention.